Radio frequency identification (RFID) systems typically comprise one or more reader powered by a battery or power supply unit and capable of communicating with RFID transponder or tags. A RFID transponder may be an active tag which is powered by a battery, or a passive tag which is powered by the high frequency field generated by the reader, or a semi active/passive tag which is activated by the high frequency field generated by the reader and uses a battery for further activities. It comprises at least electronic circuitry for storing data and communicating with a reader, and an antenna tuned with the frequency range in which the RFID transponder is operated.
Usually, different frequency ranges are provided for contact less identification systems using RFID transponder in different countries such as Japan, USA, and the European Union (EU). For example, the UHF (ultra high frequency) band, which is often used for RFID transponder, is located in the range from 902 to 928 MHz in the USA, and in the range from 863 to 868 MHz in the EU. In order to use the same RFID transponder in the USA and EU, a frequency range from about 860 MHz to about 930 MHz must be covered. U.S. Pat. No. 6,891,466 B2 discloses an antenna which is designed to cover such a broad frequency range. However, the disclosed antenna structure is a patch antenna which requires two metallization layers or a longitudinal resonator consisting of wires. These antenna structures are complex and, therefore, costly.